Specifically, for a given layer \(\ell \) , we seek to compare the features \(\mathcal {F}_t^{\ell }(O^p_k)\)  and \(\mathcal {F}_t^{\ell }(O^{gt}_k)\)  of the positive box \(k\) .
To relax the pixel-wise difference between the features, we make use of the adaptive pooling strategy of [1]}, which produces a feature map \(AP(\mathcal {F}_t^{\ell }(O))\)  of a fixed size \(M\times W \times H\)  from the features extracted within region \(O\) . We therefore write our localization distillation loss as
\(\mathcal {L}_{kd-loc} = \frac{1}{KLMHW} \sum _{k=1}^{K} \sum _{\ell =1}^{L}\mathbb {1}_\ell \Vert AP(\mathcal {F}_t^{\ell }(O^p_k)) - AP(\mathcal {F}_t^{\ell }(O^{gt}_k))\Vert _1\;,\) 
